Comparison of hydrogen embrittlement behavior of X52 and X65 steels in low-pressure gaseous hydrogen environments

Hydrogen gas is one of the most important long-term energy storage methods for renewable energy, and hydrogen utilization is also considered as an important means of achieving carbon reduction. At present, hydrogen storage and transportation under ambient-temperature and high-pressure is an important method for hydrogen energy storage and transportation. However, due to the threat of hydrogen embrittlement under high-temperature and high-pressure environment, there is a common concern over the hydrogen embrittlement of the steel pressure vessels and pipelines caused by hydrogen, which may result in unsafe consequences. In the present paper, the hydrogen charging tests, the conventional slow strain rate tensile (SSRT) tests, modified slow strain rate tensile (MSSRT) tests, and the hydrogen-induced cracking tests with the wedge-open loading (WOL) samples under ambient-temperature and high-pressure gaseous hydrogen environments were carried out for the commonly used pressure vessel steels Q345R, 30CrMo and X80 pipeline steel in China. The experimental results show that hydrogen hardly penetrates into Q345R, 30CrMo and X80 steels under ambient-temperature and 35 MPa gaseous hydrogen environment. When increasing the hydrogen pressure to 70 MPa, it is also difficult for hydrogen to penetrate the above three kinds of steels, and the maximum increase in hydrogen concentration is only about 0.1 ppm. When increasing the hydrogen pressure to 110 MPa, a small amount of hydrogen can penetrate into 30CrMo steel (the increase in hydrogen concentration is 0.38 ppm), but it is still difficult for hydrogen to penetrate into Q345R and X80 steels (the increase in hydrogen concentration is less than 0.0645 ppm). The MSSRT tests under the ambient-temperature and 35 MPa gaseous hydrogen environment show that the elongation (EL) and reduction of area (RA) of the above three kinds of steels does not decrease significantly. Compared with the MSSRT results under the ambient-temperature and 35 MPa gaseous nitrogen environment, the ELs of Q345R, 30CrMo and X80 steels decrease by 0.2%, 4.3%, and 3.2%, respectively, and the RAs of Q345R, 30CrMo and X80 steels decrease by 0.4%, 1.1%, and 1.5%, respectively. In addition, the results of the hydrogen-induced cracking tests with WOL samples show that, even if the applied stress intensity factor reaches 103 MPa·m1/2, the pre-crack of 30CrMo steel does not propagate under the ambient-temperature and 110 MPa gaseous hydrogen environment. In summary, hydrogen has almost no effect on Q345R, 30CrMo and X80 steels under the ambient-temperature and medium/high-pressure (below 35 MPa) gaseous hydrogen environment. When hydrogen pressure reaches 70 MPa, there is little difference in hydrogen permeation compared to the 35 MPa condition, thereby the influence of hydrogen on the mechanical properties of the above steels could be slight as well. When the hydrogen pressure reaches 110 MPa, the 30CrMo steel with the highest hydrogen permeation also exhibits good resistance to hydrogen induced cracking, indicating that hydrogen has limited influence on the mechanical properties of the steels.

The problem of a sudden high-pressure hydrogen jet release into a low-pressure environment is highly important in various industrial and aerospace applications that require a safe storage of pressurized hydrogen. In the present work, numerical simulations are carried out for a sudden hydrogen-jet release from a high-pressure vessel into hydrogen at atmospheric pressure through a slit. Two modeling approaches are extensively compared: 1) Full-scale solution of the entire problem, which includes the high-pressure vessel and the low-pressure hydrogen environment; 2) Simplified solution approach, which includes only the low-pressure hydrogen environment under the assumption of choked-flow conditions at the high-pressure vessel slit. It is shown in the present work that the choked-flow assumption can lead to different results from a full-scale computation. In a full-scale computation, the Mach number is subsonic at the slit exit and a "vena contracta" forms downstream of the slit exit. Both approaches are shown to capture the main flow structures, such as the lead shock, contact surface, and Mach shock. However, in the choked-slit assumption, the barrel shock is detached from the slit-exit edge and the jet expands faster than in the full-scale case.

Notched-tensile properties under high-pressure gaseous hydrogen: Comparison of pipeline steel X70 and austenitic stainless type 304L, 316L steels

3 - The Low-Pressure Gas and Vacuum Processing Environment

Experimental study on slow tensile, fatigue, and impact on X42 steel and #20 carburizing steel

Establishment of an in-situ small punch test method for characterizing hydrogen embrittlement behaviors under hydrogen gas environments and new influencing factor

The risk of hydrogen embrittlement (HE) and stress corrosion cracking (SCC) is a strong concern for material selection in the oil and gas sector. The presence of H2S enhances hydrogen charging, which can increase hydrogen embrittlement (HE) susceptibility. There are knowledge gaps about HE in the environment saturated with pure carbon dioxide (CO2) and with CO2 containing H2S. CO2 has a strong impact on corrosion rate as well, enhancing cathodic reactions. CO2 might also have a direct contribution to hydrogen charging and cracking mechanisms. This study addresses the assessment of hydrogen permeation and HE of X65 and X80 steels in CO2 and/or H2S environments. The performance of both steel grades is investigated, supported by experimental approach. The results indicate that the loss of mechanical resistance is due to hydrogen uptake and diffusion as well as the anodic dissolution, especially in Solution B. It is observed that X80 steel used in this work is more susceptible to cracking than X65 steel even in pure CO2. It is concluded that the advantage of using a higher‐mechanical‐resistant steel, X80 can be suppressed by HE effects.

X80 pipeline steel is a low carbon, micro–alloyed high–grade steel and a fairly new steel used as pipeline material in worldwide. The material has the huge potential to be used widely for building the oil/gas transmission pipelines in the 21st century because of its high intensity and high toughness. X80 steel has been adopted on the second west–east gas transmission pipeline project in China. Whereas, there is a issue, stress corrosion cracking (SCC) is more likely to occur on X80 pipeline steel, because of its high strength and fine microstructure, it will be a vital threat to safe operation of buried oil/gas pipelines. However, the related research about SCC behavior of X80 pipeline steel in high pH carbonate/bicarbonate solution is rarely reported at present. Comparing with X65 pipeline steel, X80 steel has higher strength and finer microstructure, because of these differences, it may have some certain influence on the SCC behavior of X80 steel, and even change the mechanism of high pH SCC. Consequently, it is necessary to study the SCC behavior and mechanism of X80 steel in high pH solution. In this work, the SCC behavior and mechanism of X65 and X80 pipeline steels in high pH concentrated carbonate/bicarbonate solution are investigated by slow strain rate testing (SSRT), electrochemical test and surface analysis technique. The results show that the cracking mode of X65 pipeline steel in carbonate/bicarbonate solution is intergranular SCC (IGSCC). While the mixed cracking mode of X80 pipeline steel in high pH solution is that the crack is intergranular in the early stage of the crack propagation, and transgranular SCC (TGSCC) in the later stage, which is mainly * 6r=$/= *v 51131001 B6r!n^B oQ*v 2012AA040105 :5 X^=#* : 2013–06–08, X^6 #* : 2013–09–07 B z : 0 m, y, 1985 ~?, !Q? DOI: 10.3724/SP.J.1037.2013.00315 j 12 / le : X65 A X80 /$ pH +U%bdI F(U2 f^C 1591 transgranular. The cracking mode of X80 steel is associated with the microstructure and high strength of the steel. The key reason for TGSCC occurring of X80 steel is that the decrease of pH value of the crack tip during the crack propagation process. The SCC mechanism of X65 steel in high pH carbonate/bicarbonate solution is anodic dissolution (AD) mechanism. While the SCC mechanism of X80 steel in high pH solution is mixed controlled by both AD and hydrogen embrittlement (HE) mechanisms, and the HE mechanism may play a significant role in the deep crack propagation at the later stage. The high strength X80 steel consisted of fine acicular ferrite and granular bainite has a higher susceptibility to SCC in high pH solution, comparing with low strength X65 steel composed of ferrite and pearlite.

Effect of hydrogen traps on hydrogen permeation in X80 pipeline steel —— a joint experimental and modelling study

Diamond-based low work function thermionic electron emitters are in high demand for applications ranging from electron guns and space thrusters to electrical energy converters. A key requirement of such diamond-based electron sources is hydrogen termination of the surfaces which can significantly reduce the emission barrier. However, at high temperatures (> 600°C), terminated hydrogen begins to desorb causing degradation in thermionic emission performance. The purpose of this study is to examine low-pressure hydrogen operating environments as a means to overcome this high temperature performance limitation by enabling increased thermionic emission currents with improved stability at temperatures > 600°C. A series of isothermal and isobaric experiments were performed in both nitrogen and hydrogen gas environments to determine the performance enhancement. Diamond electron emitters in both the as-grown and hydrogenated states were characterized at temperatures of 600°C, 625°C, and 650°C. An increase in thermionic emission current over vacuum operation was observed following the introduction of hydrogen. Upon evacuation of hydrogen to vacuum, the emission current decreased back to baseline levels. Further experiments in gas environments at a constant pressure (~5.5 x 10-6 Torr) were conducted at temperatures ranging from 700-900°C. It was observed that the hydrogen environment promoted increased emission current while also enabling the diamond electron emitters to stably emit at increased temperatures compared to vacuum operation. Analogous experiments using nitrogen environments did not show any measurable performance enhancements, thus verifying that hydrogen is responsible for the observed effect. These results suggest diamond-based electron emitters can have improved thermionic emission performance at temperatures > 600°C when operating in hydrogen gas environments.

The hydrogen concentration as well as the desorption energy of reversible and irreversible traps in steel can be effectively analyzed through thermal desorption spectroscopy (TDS) method. However, the thermal desorption curves are affected by sample size and heating rate. Whether the hydrogen amount and the desorption energy are affected by the heating rate and sample size are unknown. First, standard hydrogen-filled samples provided by LECO corporation were tested to ensure the stability and accuracy of the test instrument. Then, hydrogen was introduced into X80 pipeline steel cylinder samples of different sizes at 300 °C, 20 MPa gaseous hydrogen environment for 48 hours. Finally, thermal desorption tests were carried out to analyze the effect of heating rate and sample size on the desorption results of hydrogen. The results show that the sample size and heating speed have little influence on the hydrogen concentration test results, but have significant influence on the thermal desorption curve. As the specific surface area of the sample increases from 0.48 mm−1 to 0.86 mm−1, the peak temperature decreases approximately linearly. There are two obvious desorption peaks (Peak1 and Peak2) of X80 pipeline steel after hydrogen charging, and the trap desorption energy obtained from samples of different sizes is similar. The desorption energy of Peak1 trap is 13 ± 1.46 kJ/mol, which may correspond to the hydrogen traps of interstitial lattice sites, dislocations and low angle grain boundaries (LAGB). Peak2 consists of two overlapping desorption peaks (Peak2-1 and Peak2-2). the desorption energy Peak2-1 trap is 48.3 ± 14.78 kJ/mol, which may correspond to martensite/austenite (M/A) interface and dislocation nucleus. The desorption energy of Peak2-2 trap is 80.43 ± 9.98 kJ/mol, which may correspond to high angle grain boundaries (HAGB). The reversible, irreversible and total hydrogen concentration in X80 steel are 0.05 ± 0.006ppm, 0.54 ± 0.04ppm and 0.59 ± 0.04ppm, respectively. When conducting thermal desorption analysis, samples of the same size should be kept, and the heating rate should not be too fast, otherwise the overlap of different desorption peaks will cause non-negligible decoupling errors.

X80 steel is extensively used in hydrogen environments and is susceptible to hydrogen embrittlement (HE). This paper studied the hydrogen-induced cracking (HIC) behavior in the coarse-grained heat-affected zone (CGHAZ) of X80 steel welds, through applying in situ hydrogen-charging tensile experiments, hydrogen permeation experiments, and various surface analysis techniques. It is shown that a few hydrogen atoms can significantly decrease a material’s elongation and reduction of area. When the heat input (HI) was 29.2 kJ/cm, the material had minor sensitivity to hydrogen embrittlement. The tensile fractures were ductile without hydrogen. However, the fracture surface exhibited brittle fracture with hydrogen. With increased HI, the HE fracture showed a transition of intergranular fracture→intergranular and transgranular mixed fracture→transgranular fracture. In the presence of hydrogen, the grain boundaries of elongated strips were prone to the formation of intergranular cracks under a tension load, and the hydrogen embrittlement resistance of the bulk lath bainite (LB) was weak. The hydrogen embrittlement susceptibility of pure granular bainite (GB) was lower. Fine LB and GB composite structures could remarkably inhibit intergranular cracks, giving the steel a superior resistance to hydrogen embrittlement.

Experimental and molecular dynamics study of the hydrogen embrittlement behavior of X52 steel: Analysis of abnormal hydrogen embrittlement susceptibility

Comparison of hydrogen embrittlement in three pipeline steels in high pressure gaseous hydrogen environments

There are several factors that affect the strength of high-strength steel SCM435 as a sharp notched specimen in a hydrogen gas environment. In this paper, tensile tests were carried out in several hydrogen and helium gas environments. The examined factors were the gas pressure, the gas temperature, the cross-head speed and the notch root radius. The results of the tensile tests in the hydrogen gas environments showed a decrease in the tensile strengths for any given environmental factor. This was not observed in the helium gas environments. Additionally, by investigating the area of intergranular fracture, it was found that the tensile strength had a reciprocal relationship with the area of the intergranular fracture regardless of several environmental factors.